Implantable electrodes can suffer from in vivo fouling, such as due to protein adsorption to the surface of the implantable electrodes. This initial protein adsorption can trigger the beginning of an inflammatory response, which may eventually culminate as fibrotic tissue deposition at the implant site. The fibrotic tissue deposition can act as a capacitive tissue layer and can consequently lead to a gradual increase in impedance over time as the tissue continues to build. As surrounding impedance increases, the implant becomes less efficient and may require more power to operate as desired. As a result, the efficacy and/or battery lifetime of the implant may be decreased and an implant user may require follow-up surgery to replace the fouled implant.
Efforts to decrease the in vivo impedance and increase the overall lifetime of the implant can include coating the electrode in a biomaterial that resists protein adsorption, however such biomaterials can be very difficult to reliable secure to or around an electrode. Attachment can be attempted using covalent bonding between the hydrogel and an oxide layer of the electrode. However, for certain electrodes, such as noble metals, robust covalent bonding can be very challenging to achieve. These materials may not easily form an oxide layer, without which the biomaterial has no functional handle on which to reliably, chemically attach. Unreliable attachment of biomaterials can result in further problems and can result in a lower effective lifespan of the implant than desired.